Gradient refractive index encapsulant layer for enhancing light extraction efficiency of multi-chip LED packaging

Light extraction of high power LED has always been an issue for the big refractive index contrast between LED chips and encapsulant. In this work, a new structure of encapsulant with gradient refractive index is designed and tested and its mechanism is studied. High refractive index TiO2-epoxy composite is fabricated by dispersing TiO2 nanoparticles into epoxy and its properties such as transmittance and RI are measured. Optimal structure with 2 layers is demonstrated to be more effective and have higher output power than conventional structure. Some experiments are designed to verify the performances of this new structure and show that the light power of GRIN encapsulant structure increases by 7.2% compare to conventional structure. Current-dependent light power is measured to further evaluate the performance of the GRIN encapsulant structure and shows that this structure exhibits excellent high-power performance.